A semiconductor pressure sensor having a diaphragm (i.e., a diaphragm type semiconductor pressure sensor) includes a diaphragm and a strain gauge resistor. Both of the diaphragm and the strain gauge resistor are formed on a semiconductor substrate for detecting pressure. The substrate has a principal plane of (110) crystalline plane (i.e., a (110) plane). This pressure sensor is disclosed, for example, in Japanese Unexamined Patent Application Publication No. 2001-356061 (i.e., U.S. Pat. No. 6,601,452). Specifically, the diaphragm is formed on the principal plane of the substrate, and detects pressure. The strain gauge resistor is formed on the diaphragm, and provides a bridge circuit for outputting a detected signal corresponding to a distortion of the diaphragm.
Here, another pressure sensor having a pair of center gauge resistors and a pair of side gauge resistors is disclosed in Japanese Unexamined Patent Application Publication No. H11-94666 (i.e., U.S. Pat. No. 6,595,065). In this sensor, the strain gauge resistors, i.e., the center gauge and side gauge resistors, are disposed on the (110) plane of the substrate. The center gauge resistors are disposed on the center of the diaphragm, and disposed along with a <110> crystalline axis (i.e., a <110> axis). The side gauge resistors are disposed on a periphery of the diaphragm.
In the above sensors, a glass base is bonded to the substrate with using an anodic bonding method and the like. The thermal expansion coefficient of the substrate is different from that of the glass base. Therefore, when temperature around the sensor changes, a thermal stress is generated between the substrate and the glass base. The thermal stress may distort the diaphragm, so that resistance of each resistor disposed on the diaphragm is changed in proportion to the distortion. The thermal stress applied to each resistor is different each other since the resistor is disposed on a different position on the diaphragm. Specifically, the thermal stress applied to each center gauge resistor is different from the thermal stress applied to each side gauge resistor. Thus, a difference between the thermal stress applied to the center gauge resistor and the thermal stress applied to the side gauge resistor provides a detection error as a noise. Further, the difference of the thermal stress changes nonlinearly in relation to the temperature, so that the temperature dependence of offset of the output voltage has a certain curvature in relation to the temperature. Therefore, in the temperature dependence of the offset of the output voltage, a slope of the offset of the output voltage in relation to the temperature between a room temperature and a certain high-temperature is different from that between a certain lower temperature and the room temperature. This difference of the slope is called as a temperature nonlinearity offset (i.e., TNO) property. The TNO property is a property of the offset of the output voltage having nonlinearity in relation to the temperature. The TNO property is one of the most important factors for deciding an accuracy of the sensor.
Further, when the pressure sensor is minimized in size, i.e., the substrate is minimized, it is considered that the diaphragm is required to be minimized. That is because the diaphragm constitutes a large area in the sensor. In this case, the difference of the thermal stress between the center gauge resistors and the side gauge resistors becomes larger, so that the detection error becomes larger. Thus, as the diaphragm becomes smaller, the TNO property becomes worse, i.e., the difference of the slope becomes larger. Therefore, it is difficult to minimize the sensor without deteriorating the TNO property.